Permanent magnet machines, and in particular DC brushless permanent magnet machines can be implemented as an electric modulated pole machine. In recent years electric machine designs evolved from modulated pole machines, claw pole machines, Lundell machines and transverse flux machines (TFM), have become more and more interesting. Electric machines using the principles of these machines were disclosed as early as about 1910 by Alexandersson and Fessenden. One of the most important reasons for the increasing interest is that the design enables a very high torque output in relation to, for example, induction machines, switched reluctance machines and even permanent magnet brushless machines. Further, such machines are advantageous in that the coil often is easy to manufacture. Examples of implementations of the modulated pole machine topology include implementations as e.g. Claw-pole-, Crow-feet-, Lundell- or TFM-machines. The flux concentrating rotor is generally speaking built up by a number of pole pieces of a soft magnetic material and an equal number of permanent magnets in between. The permanent magnets are magnetised in a circumferential direction with every second magnet having a reverse magnetisation vector direction.
State of the art rotor design use high performance NeFeB magnets to maximize the pole field strength and to minimize the performance to weight of the structure. One alternative is to use a lower performing less costly magnet but then the magnet cross-section area must be proportionally increased to achieve equal magnetic pole strength. The presently known way of arranging the lower performing magnet is to increase the rotors all over radial dimensions that will result in increased weight and moment of inertia of the rotor. The intermediate soft magnetic pole pieces must also be radially extended to be able to pick up the magnetic flux from the permanent magnets.
It is desirable to improve the performance of the electric machine and/or to reduce the production cost of such a machine without reducing its oerformance.